Summer of code 2017: Python, Day 18 Iterables

A comprehension is a list, a set or a dictionary that is computed via a set of looping and filtering instructions. The comprehension consists of a single expression followed by at least one for clause and zero or more for or if clauses

List Comprehensions

The basic syntax for list comprehensions looks like this

[expr(item) for item in iterable]

Here is an example in code, the code below returns the length for each item in the list

We can make it more interesting by using a condition and only return the key value pair if the price is the max price for that ticker. I added a price of 1000 for AAPL and a price of 5000 for F. As you can see in the code below, I have used a filtering predicate if max(price)

When no more data is available a StopIteration exception is raised instead. At this point, the iterator object is exhausted and any further calls to its __next__() method just raise StopIteration again.